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  <div class="titlepage"><div><div><h1 style="clear: both"><code>value_or_error&lt;T&gt;</code></h1></div></div></div>
  <p>If on C++ 20 or the Concepts TS is enabled, a boolean concept matching types with a public <code>.has_value()</code> observer which returns <code>bool</code>, a public <code>.value()</code> observer function, and a public <code>.error()</code> observer function.</p>

<p>If without Concepts, a static constexpr bool which is true for types matching the same requirements, using a SFINAE based emulation.</p>

<p>This concept matches expected-like types such as 
<a href="https://wg21.link/P0323" class="api-reference" target="_blank"><i class="fa fa-book" aria-hidden="true"></i> P0323 <code>std::expected&lt;T, E&gt;</code></a>
, one of which is <a href="../../reference/types/basic_result.html" class="api-reference"><code>basic_result&lt;T, E, NoValuePolicy&gt;</code></a>
. Be aware it does not differentiate between value-<em>or</em>-error types and value-<em>and</em>-error types if they present the interface matched above.</p>

<p>If you want a concept matching specifically <a href="../../reference/types/basic_result.html" class="api-reference"><code>basic_result&lt;T, E, NoValuePolicy&gt;</code></a>
, see <a href="../../reference/concepts/basic_result.html" class="api-reference"><code>basic_result&lt;T&gt;</code></a>
.</p>

<p><em>Namespace</em>: <code>BOOST_OUTCOME_V2_NAMESPACE::concepts</code></p>

<p><em>Header</em>: <code>&lt;boost/outcome/convert.hpp&gt;</code></p>

<p><em>Legacy</em>: This was named <code>convert::ValueOrError&lt;T&gt;</code> in Outcome v2.1 and earlier. Define <a href="../../reference/macros/enable_legacy_support_for.html" class="api-reference"><code>BOOST_OUTCOME_ENABLE_LEGACY_SUPPORT_FOR</code></a>
 to less than <code>220</code> to enable.</p>


        </div><p><small>Last revised: August 19, 2020 at 12:15:40 &#43;0100</small></p>
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